This invention relates generally to fire extinguishing systems, and more particularly, to expansion nozzle assemblies used to dispense foam in a fire extinguishing system.
Enclosed areas such as cargo holds within an airplane, inside cargo containers held within the cargo hold of an airplane, computer rooms, equipment rooms, and the like all may contain combustible materials which need to be extinguished during a fire. The type of combustible material and the use of the enclosed area may determine how a thermal event is extinguished.
Different types of fire extinguishing systems exist. A cargo hold, for example, may use a high or medium foam expansion system while a commercial office building may use a sprinkler system. In a foam expansion system, an expansion nozzle expands a foam solution into a blanket of foam bubbles. The nozzle may extend within a discharge tube and accepts the foam solution from a container under pressure or from an atmospheric tank and pump assembly. The discharge tube may be open or have an opening to the atmosphere or ambient air proximate the end where the foam solution is introduced, or may have orifices open to the atmosphere along the discharge tube.
When the system is activated, the foam solution is discharged into the nozzle. The nozzle sprays the foam solution in a spray pattern onto a screen at an opposite end of the discharge tube. The pressure in the discharge tube results in a Venturi effect, pulling air into the discharge tube and causing bubbles to form on an opposite side of the screen. The bubbles are released into the atmosphere through an open end of the discharge tube. When the bubbles break, the atmosphere or room air within the bubbles is released. The foam solution provides a wetting and extinguishing effect, but does not create an inert atmosphere in which combustion cannot take place. Therefore, combustible materials may re-kindle as a result of deep-seated combustion.
Other fire extinguishing systems attempt to maintain an atmosphere in which combustion cannot take place by injecting inert gas into the enclosed area. The inert gas mixes with and displaces the ambient air, and thus escapes or leaks from the enclosed area with the ambient air, making it difficult to maintain a desired percentage of inert gas. Optionally, intermittent additional discharges of inert gas or a slow continuous discharge of inert gas after the initial discharge may be used to compensate for the leakage. This requires a more complicated discharge system and more inert gas is needed.
Thus, the bubbles enclosing ambient air and/or the injection of inert gas as discussed above may not maintain a desired inerting atmosphere within the enclosed area. The inert gas may easily escape the area and is diluted with air. Also, adding additional gas periodically or continuously to maintain the inerting atmosphere requires more product and is thus more expensive.
Therefore, a need exists for an apparatus to maintain an inerting atmosphere in an enclosed area. Certain embodiments of the present invention are intended to meet these needs and other objectives that will become apparent from the description and drawings set forth below.